Switching Materials On Command
You need to do all this on one material. Applying materials to individual faces is not going to work for rapid testing.

Once you are using only one material toggling On and off is easy and changing the color is super simple.

First off you will need a mask to differentiate what parts of the mesh will get what. I'd recommend using an image (easy to paint in texture paint mode and transferable to any game engine), but you can also use vertex colors, or proxy objects inside blender.

For my example I'm using an image, and vertex colors.

The image texture node is the mask I painted. The key to the toggling is the MixRGB node(s). The Value input node is what I'm using to control the toggling. When the value is 0 the MixRGB node is outputting 100% black, which is feed into the Fac for the Mix Shader node. (0 uses the top socket, 1 is the bottom socket) Likewise when the value is changed to 1,  the MixRGB outputs the mask image which has white painted in the proper places. Thus the Emission shader gets to shine.

Its the exact same thing for the one I have labeled "Engine toggle" except here I'm using the vertex colors as the mask instead of an image.

The RGB input is how I'm changing the color of the "lights." You could also use a image and a special UV map just to re color (You would simply move the UVs to a different color) but for in blender the node is much easier.



The nodes can look much neater when wrapped in a node group, but for testing I prefer access straight to the nodes.